Total Dynamic Head (TDH)
Total dynamic head (TDH) is the total energy per unit weight that a pump must add to a liquid to move it through a given system, expressed as a height of liquid column in metres or feet. It is the sum of the static head (elevation difference between the liquid surfaces at source and destination), the pressure head difference between suction and discharge vessels, friction losses in pipes, valves and fittings, and the velocity head difference. Because friction loss increases approximately with the square of flow, TDH plotted against flow forms the system curve; the pump operates where this curve intersects its head–capacity curve. Expressing head rather than pressure makes a pump curve independent of liquid density. Accurate TDH calculation is essential for pump sizing, motor selection and avoiding operation far from the best efficiency point.
Examples
- Sizing a transfer pump between two storage tanks
- Calculating head for a high-rise building booster set
- Plotting a system curve for a cooling water loop